This invention relates to a data transmission method wherein a plurality of optical signals obtained by converting a plurality of digital data representative of video signal information or like information into serial data and then opto-electrically converting the serial data are bidirectionally transmitted between two transmission/reception sections through an optical signal transmission cable and a data transmission apparatus for carrying out the data transmission method.
In the field of video signals, digitalization is proceeding in order to achieve diversification of transmission information and higher picture quality of reproduction images. For example, a high definition television (HDTV) system which handles a digital video signal formed from digital data representative of video signal information has been proposed. A digital video signal under the HDTV system (a signal of the type mentioned is hereinafter referred to as HD digital video signal) is formed, for example, in accordance with specifications established by the BTA (Broadcasting Technology Association). According to the specification, a digital video signal of the Y, PB/PR format and another digital video signal of the G, B, R format are available. In the digital video signal of the Y, PB/PR format, Y signifies a luminance signal, and PB and PR signify color difference signals. Meanwhile, in the digital video signal of the G, B, R format, G, B, and R signify a green primary color signal, a blue primary color signal and a red primary color signal, respectively.
The HD digital video signal of the Y, PB/PR format has a frame rate of 30 Hz or 30/1.001 Hz (in the present specification, both rates are referred to as 3.;/;./0 Hz) and is a signal for interlaced scanning wherein each frame image is formed separately in a first field image and a second field image. The digital video signal of the Y, PB/PR format is formed, for example, with such a data format as illustrated in FIGS. 21A and 21B. The data format illustrated in FIGS. 21A and 2B includes a luminance signal data string (Y data string) representative of luminance signal information of the video signal as seen in FIG. 21A and a color difference signal data string (PB/PR data string) representative of color difference signal information as seen in FIG. 21B. Each of the Y data string and the PB/PR data string has a quantization bit number of 10, and accordingly, each of data words which form the data strings has a 10-bit configuration. Further, each of the Y data string and the PB/PR data string has a word transmission rate of, for example, 74.25 MBps. FIG. 21A illustrates a line blanking part in a line part of the Y data string and part of video data parts forwardly and rearwardly of the line blanking part. FIG. 21B illustrates a line blanking part in a line part of the PB/PR data string and part of video data parts forwardly and rearwardly of the line blanking part.
In the Y data string, each video data part is preceded by timing reference code data (SAV: Start of Active Video) of 4 words (3FF(Y), 000(Y), 000(Y), XYZ(Y); 3FF, 000 and XYZ are hexadecimal representations, and (Y) represents that the word is included in the Y data string) each having a 10-bit configuration. Further, each video data part is followed by another timing reference code data (EAV; End of Active Video) of 4 words (3FF(Y), 000(Y), 000(Y), XYZ(Y)) each having a 10-bit configuration. Similarly, also in the PB/PR data string, each video data part is preceded by timing reference code data SAV of 4 words (3FF(C), 000(C), 000(C), XYZ(C); 3FF, 000 and XYZ are hexadecimal representations, and (C) represents that the word is included in the PB/PR data string) each having a 10-bit configuration. Further, each video data is followed by another timing reference code data EAV of 4 words (3FF(C), 000(C), 000(C), XYZ(C)) each having a 10-bit configuration. Naturally, each of the timing reference code data EAV and SAV in the Y data string is disposed in each of the line blanking parts in the Y data string, and each of the timing reference code data EAV and SAV in the PB/PR data string is disposed in each of the line blanking parts in the PB/PR data string.
In the four words (3FF, 000, 000, XYZ) shown with (Y) or (C) added thereto, the first three words (3FF, 000, 000) are provided for establishing word synchronism or line synchronism. Meanwhile, the last one word (XYZ) is provided for identification between the first field and the second field in the same frame or for identification between the timing reference code data SAV and the timing reference code data EAV. This similarly applies to the following description.
Also the HD digital video signal of the G, B, R format is a signal for interlaced scanning having a frame rate of 30 Hz and is formed with such a data format, for example, as illustrated in FIGS. 22A, 22B, and 22C. The data format illustrated in FIGS. 22A, 22B, and 22C includes a green primary color signal data string (G data string) of the video signal as seen in FIG. 22A, a blue primary color signal data string (B data string) of the video signal as seen in FIG. 22B, and a red primary color signal data string (R data string) of the video signal as seen in FIG. 22C. The G data string represents green primary color signal information. The B data string represents blue primary color signal information. The R data string represents red primary color signal information. Each of the G, B, and R data strings has a quantization bit number of 10, and accordingly, each of data words which form the data strings has a 10-bit configuration. Further, each of the G, B, and R data strings has a word transmission rate of, for example, 74.25 MBps. FIGS. 22A, 22B, and 22C illustrate a line blanking part in a line part of the G, B, and R data strings, respectively, and part of video data parts forwardly and rearwardly of the line blanking part.
In each of the G, B, and R data strings, each video data part is preceded by timing reference code data SAV of 4 words (3FF(G), 000(G), 000(G), XYZ(G); (G) represents that the word is included in the G data string, 3FF(B), 000(B), 000(B), XYZ(B); (B) represents that the word is included in the B data string, 3FF(R), 000(R), 000(R), XYZ(R); (R) represents that the word is included in the R data string) each having a 10-bit configuration. Further, each video data part is followed by another timing reference code data EAV of 4 words (3FF(G), 000(G), 000(G), XYZ(G); 3FF(B), 000(B), 000(B), XYZ(B); or 3FF(R), 000(R), 000(R), XYZ(R)) each having a 10-bit configuration. Naturally, each of the timing reference code data EAV and SAV in the G, B, and R data strings is disposed in each of the line blanking parts in the G, B or R data string.
The existing HDTV system employs an HD digital video signal of the Y, PB/PR format or the G, B, R format for interlaced scanning having a frame rate of 30 Hz as described above. In contrast, as an HDTV system of a next generation, a system is proposed which employs an HD digital video signal of the Y, PB/PR format or the G, B, R format for progressive scanning having a frame rate of 60 Hz or 60/1.001 Hz (in the present specification, both rates are referred to as 60 Hz). According to the progressive scanning, each frame image is formed without being divided into first and second fields. The HD digital video signal of the Y, PB/PR format or the G, B, R format for progressive scanning is called HD digital video signal of the progressive type.
It has been proposed to standardize the format of digital data which form an HD digital video signal of the progressive type having a frame rate of 60 Hz with the standards SMPTE 274M established by the SMPTE (Society of Motion Picture and Television Engineers) of the United States. The format standardized by the SMPTE 274M includes prescriptions of a frame rate: 60 Hz, an effective data sample number per line: 1.920, an effective line number per frame: 1.080, a sampling frequency: 148.5 MHz or 148.5/1.001 MHz (in the present specification, both frequencies are referred to as 148.5 MHz), and a quantization bit number: 8 or 10. Further, the parallel data interface uses 8 bits×2=16 bits or 10 bits×2=20 bits for the Y, PB/PR format, but uses 8 bits×3=24 or 10 bits×3=30 bits for the G, B, R format.
In digital data which form a digital video signal whose quantization bit number is 8 or 10 as just described, a code which is not used to represent video signal information is defined as an inhibition code. For example, where the quantization bit number is 8, 00h and FFh (the suffix h represents that the numeral is a hexadecimal representation), that is, 0000 0000, and 1111 1111, are defined as inhibition bits. Meanwhile, where the quantization bit number is 10, 000h to 003h, and 3FCh to 3FFh, that is, 00 0000 0000 to 00 0000 0011 and 11 1111 1100 to 11 1111 1111, are defined as inhibition codes.
It is to be noted that, in the Y, PB/PR format, the sampling frequency of each of the PB data string and the PR data string is ½ that of the Y data string. In the following description, the Y, PB/PR format is suitably represented as 4:2:2 format. Meanwhile, in the G, B, R format, the sampling frequencies of the G, B, and R data strings are equal to each other. In the following description, the G, B, R format is suitably represented as 4:4:4 format.
Separately from such an HD digital video signal as described above, a digital video signal of the progressive type is proposed for producing moving pictures of a cinema to be projected, for example, through a film including 24 frames per second with picture quality equal to that of an image obtained by the HDTV system. Such a digital video signal as just described is hereinafter referred to as D-Cinema signal.
The D-Cinema signal can be considered as a digital video signal of the progressive type which has a frame rate of, for example, 24 Hz or 24/1.001 Hz (in the present specification, both rates are referred to as 24 Hz). However, the frame rate of the D-Cinema signal is not limited to 24 Hz, but may be 25 Hz, 30 Hz, 50 Hz, 60 Hz or some other rate. Digital data which form a digital video signal whose frame rate is 24 Hz, 25 Hz, 30 Hz, 50 Hz, 60 Hz or some other rate are standardized in terms of the format by the SMPTE 274M. In particular, the format includes prescriptions of an effective data sample number per line: 1920, an effective line number per frame: 1080, a sampling frequency: 74.25 MHz or 74.25/1.001 MHz (in the present specification, both frequencies are referred to as 74.25 MHz) or 148.5 MHz, and a quantization bit number: 8 or 10. Further, the parallel data interface uses 8 bits×2=16 bits or 10 bits×2=20 bits for the 4:2:2 format, but uses 8 bits×3=24 bits or 10 bits×3=30 bits for the 4:4:4 format.
Further, separately from the HD digital video signal and the D-Cinema signal described above, a different digital video signal of the progressive type (hereinafter referred to as 720P signal) has been proposed. The 720P signal has a frame rate set to 60 Hz and an effective line number set to 720 for each frame and further has an effective data sample number set to 1280 for each line. Digital data which form the 720p signal are standardized in terms of the format by the SMPTE 296M established by the SMPTE. The format standardized by the SMPTE 296M includes prescriptions of a frame rate: 60 Hz, an effective line number per frame: 720, an effective data sample number per line: 1280, a line number per frame: 750, a sampling frequency: 74.25 MHz, and a quantization bit number: 8 or 10. Further, the parallel data interface uses 8 bits×2=16 bits or 10 bits×2=20 bits for the Y, PB/PR format, but uses 8 bits×3=24 bits or 10 bits×3=30 bits for the G, B, R format.
The 720P signal was proposed during a transition period to HD digital video signals in the field of digital video signals. While the effective line number per frame and the effective data sample number per line of the HD digital video signal are 1080 lines and 1920 samples, respectively, those of the 720P signal are 720 lines and 1280 lines which are equal to two thirds those of the HD digital video signal, respectively. Therefore, while the 720P signal is inferior to the HD digital video signal in terms of the resolution of an-image reproduced based thereon, since the frame rate is 60 Hz, the 720P signal is suitable for utilization as a signal representative of images which exhibit a quick movement.
In such a situation as described above, it becomes demanded to further improve, for example, the resolution of an image reproduced based on digital data which form a digital video signal such as the HD digital video signal, D-Cinema signal or 720P signal. To this end, it is demanded to set the quantization bit number to a higher bit number than the bit number 8 or 10 used in the past, for example, to 12 bits, 14 bits or 16 bits. However, although existing standards for digital data which form a digital video signal including the SMPTE 274M and the SMPTE 296M standardize digital data whose quantization bit number is 8 or 10, they do not standardize quantization bit numbers exceeding 8 or 10, such as, for example, bit numbers of 12, 14, and 16.
Further, digital data which form a digital video signal whose quantization bit number is 12, 14 or 16 involves a problem regarding transmission. In particular, for transmission of digital data which form a digital video signal, it is desired to use serial transmission wherein the digital data are transmitted after converted into serial data. At present, however, only it is standardized that digital data which form an HD digital signal of the 4:2:2 format whose quantization bit number is 8 or 10 are transmitted using the HD SDI (High Definition Serial Digital Interface) according to the standards BTA S-004 established by the BTA mentioned hereinabove. On the other hand, nothing is standardized for serial transmission of digital data of the other formats such as, for example, digital data which form a digital video signal of the 4:4:4 format or digital data which form a digital video signal whose quantization bit number exceeds 10.
In connection with a video signal whose digitalization is proceeding as described above, a Key signal has been proposed which is used for synthesis of a video signal with another video signal. The Key signal is a signal representative of the opacity or transparency of the related video signal and is recommended in the “SMPTE RECOMMENDED PRACTICE” RP 157-1995.
In the Key signal relating to a digital video signal of the 4:2:2 format, a Key signal data string representative of digital data which form the Key signal has a format equivalent to that of a Y data string included in the digital data which form the digital video signal. Thus, the Key signal data string is handled similarly to the Y data string. Meanwhile, in the Key signal relating to a digital video signal of the 4:4:4 format, a Key signal data string representative of digital data which form the Key signal has a format equivalent to that of a G data string included in the digital data which form the digital video signal. Thus, the Key signal data string is handled similarly to the G data string.
It is sometimes demanded to transmit, upon transmission of digital data which form a digital video signal of the 4:2:2 format or the 4:4:4 format, digital data which form the digital video signal and a Key signal data string relating to the digital data. In such an instance, the following conditions are demanded from the point of view of facilitation in carrying out of the transmission and reduction of the cost. In particular, it is demanded that, in addition to digital data which form a digital video signal of the 4:2:2 format or the 4:4:4 format, a Key signal data string relating to the digital data be transmitted as an additional information data string incidental to the digital data which form the digital video signal to be transmitted. Also it is demanded that such transmission of digital data and a relating Key signal data string as just described be performed utilizing existing circuit components used for serial transmission of digital data which form, for example, a digital video signal whose quantization bit number is 10.
Details of various D-Cinema signals whose quantization bit number is 10, 12, 14, and 16 are, for example, such as illustrated in FIG. 23. Meanwhile, details of various 720P signals whose quantization bit number is 10, 12, 14, and 16 and combinations of such 720P signals and Key signals are, for example, such as illustrated in FIG. 24.
The digital video signal such as a D-Cinema signal or a 720P signal as described above or a digital video signal of the type mentioned and a Key signal are obtained, for example, from a video camera which performs an image pickup operation to form a video signal. The digital video signal or the digital video signal and the Key signal are then supplied to a signal recording and reproduction section which includes a video tape recorder (VTR) which records and reproduces the digital video signal or the digital video signal and the Key signal when necessary.
Upon image pickup by a video camera and recording and/or reproduction of a video signal from the video camera by the signal recording and reproduction section, for recording of broadcasting program information by a television broadcasting station or the like, usually a plurality of video cameras are used and form a camera section. Video signals or video signals and Key signals obtained from the video cameras which form the camera section are sent to the signal recording and reproduction section.
When the plurality of video cameras of the camera section are used for image pickup, it is necessary for each person (cameraman) who operates one of the video cameras to know an image pickup situation by the other video cameras. To this end, reproduction images based on image signals obtained from the other video cameras are displayed on an image monitor provided for each of the video cameras. Therefore, the video signals obtained from the video cameras and sent to the signal recording and reproduction section are subject a to predetermined process in the signal recording and reproduction section. Then, the video signals processed in this manner are supplied from the signal recording and reproduction section to the camera section formed from the plurality of video cameras.
The video signals supplied to the camera section formed from the plurality of video cameras are used for image reproduction on the image monitor provided for each of the video cameras of the camera section. Therefore, it is not demanded that reproduction images based on the video signals have particularly high quality. Therefore, such video signals derived from the other video cameras are obtained by performing a compression process and so forth to limit the transmission capacity thereof, and thereby facilitating transmission. In the following description, a video signal obtained, for example, by performing a compression process for a video signal is referred to as return video signal.
In this manner, between the camera section and the signal recording and reproduction section, bidirectional transmission of video signals or video signals and Key signals and a return video signal is performed. More particularly, video signals or video signals and Key signals obtained from the plurality of video cameras of the camera section are transmitted to the signal recording and reproduction section which includes a VTR. Meanwhile, a return video signal for which predetermined processing has been performed is transmitted from the signal recording and reproduction section to the camera section. Typically, a plurality of return video signals are transmitted.
Where each of the video signals obtained from the plurality of video cameras of the camera section is, for example, a D-Cinema signal or a 720P signal, the return signal is also a digital signal, that is, a digital return signal. When the D-Cinema signals or 720P signals and the digital return signals are transmitted, they are transmitted in the form of serial digital data.
As possible measures, the D-cinema signals or 720P signals or the D-Cinema signals or 720P signals and the Key signals obtained from the plurality of video cameras which form the camera section and the digital return video signals are bidirectionally transmitted between the camera section and the signal recording and reproduction section in the following manner. In particular, digital data which form the D-Cinema signal or 720P signals or the D-Cinema signals or 720P signals and the Key signals and digital data which form the digital return video signals are converted individually into optical signals. Then, the optical signals are transmitted through an optical signal transmission cable which has a great transmission signal capacity and exhibits a high transmission efficiency. In this instance, the optical signal transmission cable for interconnecting the camera section and the signal recording and reproduction section may be formed using an optical fiber.
An optical fiber used for formation of such an optical signal transmission cable as described above typically is a quartz single mode fiber, that is, a quartz SMF. The quartz SMF typically has a core diameter of 10 ″m and a clad diameter of 125 ″m and has a single propagation mode. The quartz SMF has characteristics that the transmission frequency band is wide and that the propagation loss can be suppressed low. Accordingly, the quartz SMF can be applied advantageously to high-speed long-haul communication by an optical signal and is suitable for transmission of an optical signal based on a digital video signal obtained from a video camera.
The quartz SMF exhibits attenuation of an optical signal in accordance with an attenuation characteristic illustrated in FIG. 25 and exhibits dispersion of an optical signal in accordance with a dispersion characteristic illustrated in FIG. 26. The dispersion of an optical signal is spread of a frequency spectrum of the optical signal and spread or waveform distortion of the propagation time of the optical signal caused by the material and the structure of the optical fiber. The attenuation characteristic illustrated in FIG. 25 exhibits a minimum value of attenuation with respect to light having a wavelength of approximately 1.3 ″m and light having another wavelength of approximately 1.5 ″m. Meanwhile, the dispersion characteristic illustrated in FIG. 26 exhibits minimum dispersion with respect to light having a wavelength of approximately 1.3 ″m.
When digital data which form digital video signals including D-Cinema signals, 720P signals or the like or such digital video signals and Key signals obtained from a plurality of video cameras which form a camera section and digital data which form digital return video signals are individually converted into optical signals and the optical signals are bidirectionally transmitted between the camera section and a signal recording and reproduction section using an optical signal transmission cable as described above, a plurality of optical signals are bidirectionally transmitted between the camera section and the signal recording and reproduction section. Accordingly, where a conventional data transmission technique is used, serial transmission of digital data which form digital video signals including D-Cinema signals or 720P signals or such video signals and Key signals requires parallel arrangement of a large number of optical signal transmission cables between the camera section and the signal recording and reproduction section. This also arises from the fact that it cannot be avoided to transmit the digital data which form the digital video signals or the digital video signals and Key signals divisionally in a plurality of channels. Such arrangement of a large number of optical signal transmission cables requires a great cable installation space and a high cost.
Therefore, a data transmission system is demanded which can use a single optical signal transmission cable to achieve efficient bidirectional transmission, between the camera section and the signal recording and reproduction section, of a plurality of optical signals obtained by conversion of digital data which form digital video signals including D-Cinema signals, 720P signals or the like and such digital video signals and Key signals obtained individually from a plurality of video cameras which form the camera section and digital data which form digital return video signals. However, no data transmission system of the type described is conventionally available.